Method of and apparatus for the controlled mixing of two reactive components

ABSTRACT

A method of and an apparatus for the mixing of two interactive components, especially two components adapted to form a castable synthetic resin such as a caprolactam system wherein the components are to be combined in a high-volume ratio wherein the components are circulated along closed paths at superatmospheric pressures and, by pressure increases in the respective paths, are discharged through injection nozzles into a mixing chamber.

limited States Patent [191 Biiclrmann et al.

[ METHOD OF AND APPARATUS FOR THE CONTROLLED MIXING OF TWO REACTIVECOMPONENTS [75] Inventors: Alfred Biickmann; Rudi Keuerleber,

both of Munich, Germany [73] Assignee: Krauss-Maffei AG, Munich, Germany[22] Filed: Apr. 5, 1972 [21] Appl. No.: 241,122

[30] Foreign Application Priority Data Apr. 6, 1971 Germany 2116665 [52]US. Cl 259/4, 137/563, 137/606, 239/127, 259/95, 425/425 [51] Int. Cl.BOlf 5/04, 1301f 15/02 [58] Field of Search 259/4, 18, 95; 137/563, 604,606; 222/318; 239/12'7; 425/425 [56] References Cited UNITED STATESPATENTS Breer et a1 259 4 x ,lan.8,1974l 3,424,439 1/1969 Baker 259/43,605,183 9/1971 Heckrotte 3,617,029 11/1971 Breer et a1. 259/18 FOREIGNPATENTS OR APPLICATIONS 2,046,641 9/1970 Germany Primary ExaminerBillyJ. Wilhite Assistant Examiner-Alan l. Cantor Att0rneyKarl F. Ross 5 7ABSTRACT A method of and an apparatus for the mixing of two interactivecomponents, especially two components adapted to form a castablesynthetic resin such as a caprolactam system wherein the components areto be combined in a high-volume ratio wherein the components arecirculated along closed paths at superatmospheric pressures and, bypressure increases in the respective paths, are discharged throughinjection nozzles into a mixing chamber.

15 Claims, 2 Drawing Figures 1 METHOD OF AND APPARATUS FOR THECONTROLLED MIXING OF TWO REACTIVE COMPONENTS FIELD OF THE INVENTION Ourpresent invention relates to a method of and to an apparatus for thecontrolled or metered mixing of two or more components, especiallyreactive fluids and, more particularly, to a method for the dosed mixingof fluid components of a caprolactam system for rotational casting.

BACKGROUND OF THE INVENTION For many purposes, it has been desired tomix two or more components of a reaction system under conditionsinvolving the metering and dosing of the two components with greataccuracy. The problem is most pronounced when the mixing ratio (i.e.,the volume ratio of the predominant component to the minority component)is high, e.g., of the order of 200:1 and greater. Such high mixingratios require the discharge ofa large volume of the predominatingcomponent and a much smaller discharge of the minority component intothe mixing chamber under conditions which will maintain the ratio andallow both metering operations to be carried out with accuracy.

The problem arises, to a considerable extent, in the preparation oftwo-component or multicomponent synthetic-resin systems for molding orcasting, it being advantageous to maintain the components apart untiljust prior to the forming operation. For example, in the rotationalcasting of pipes and like articles of polymerized caprolactam, thepredominating component is the monomeric lactam, while other componentsmay in clude activators and catalysts. In the caprolactam system, aconventional catalyst for a conventional activator must be combined withthe monomeric lactam before the latter will polymerize and set.

In earlier rotational casting systems, the components have been mixed byinjection after being subjected to different thermal conditions(preheating or storing temperatures). To overcome the disadvantagesobtaining when the volume ratio is high, as discussed above, it has beenthe practice to divide the anionically polymerizable caprolactam betweentwo storage vessels, to mix the activator with a portion of thecaprolactam in one of these vessels and to mix the catalyst with theother portion of the caprolactam. The two portions are the combined in amixing chamber by injection under pressure. The mixing head or chambermay be maintained under an appropriate mixing temperature while thecontents of the two storage vessels are maintained under respectivetemperatures. Pumps between the storage vessel and the mixing chamberforce the two portions through injection nozzles under injectionpressure into the mixing chamber.

While this system eliminates the difficulties encountered with thehandling of small quantities of the minor components, it has somesignificant disadvantages. Firstly, the system requires two largevessels and thus considerable residues remain in the vessels even whenthe latter have been drained by the pumps to the maximum extenttechnologically feasible. Secondly, the requirement for two largevessels, with appropriate heating and temperature-control means,increases the capital cost of the installation. Thirdly, since thecatalyst is premixed with one portion of the predeterminating component,while the activator is premixed with the other portion, there is noleeway for adjusting the proportion of, for example, the catalyst oncethe premixing step has taken place.

A further disadvantage of the system described above is that thedisplacement takes place by turning on a pump. Becauseof the inertia ofthe system (flow inertia as well as mechanical inertia), the metering ofthe components may be inaccurate and it may not be possible to obtainthe desired injection relationships. The precision of the system isfound to be poor, especially when flexible conduits connect the pumpand/or the associated storage receptacle with the mixing chamber.

OBJECTS OF THE INVENTION It is the principal object of the presentinvention to provide an improved method of mixing two components underpressure, especially two reactive components adapted to form ahardenable system for rotational casting.

Yet another object of the invention is to provide an improved method ofpreparing a mixture of two or more reactive components whereby thedisadvantages of the earlier systems described above can be obviated.

It is also an object of the invention to provide an improved apparatusfor mixing two fluid components and for carrying out the methoddescribed.

SUMMARY OF THE INVENTION We have now found that these objects can beattained conveniently and simply, and that it is possible to mix underpressure a large-volume (predominating) component and a small volume(minor) component when at least one of the components is displaceddynamically along a path under a superatmospheric pressure which is,however, below the injection-mixing pressure, and the pressure alongthis path is suddenly (instantaneously) increased by blocking flow ofthe fluid component away from an upstream portion of the path; the fluidcomponent is fed at the elevated pressure to the mixing chamber,preferably through a pressure-responsive valve, simultaneously with theinjection of the other component into the chamber. At least thelow-volume or minor component is displaced in this fashion, butpreferably both components are displaced and, advantageously, circulatedalong respective closed paths.

According to a particular feature of this invention, the components tobe mixed include caprolactam capable of anionic polymerization forrotational casting in a ratio by volume of about 200:1 to the activatorand catalyst, the ratio being generally higher. The lowvolume component,preferably at least one, but possibly both, are displaced under pressurealong respective paths which are separated and are under dynamic flowpressure below the injection-mixing pressure, the pressure in the pathsbeing increased to the mixing pressure simultaneously with injection.While we may use three paths for the components (caprolactam, catalystand activator) it is preferred to mix the catalyst in a ratio of 200:1parts to 0.5 part or greater with the caprolactam component and to mixthe resulting combination with the activator circulated along a closedpath at a dynamic pressure of about 10 atmosphere below theinjection-mixing pressure.

The dynamic pressure described above is preferably produced, at least inthe case of the low-volume component, by throttling the flow thereofprior to its return to a storage vessel, the pressure increase beingeffected by an instantaneously triggerable blocking valve between apassage communicating with the mixing chamher and this throttle.

The advantage of the system described above resides in the use of asingle large receptacle for the principal component, preferably themonomeric lactam described above. The latter can be conveniently heatedand stored independently of the proportion of the lowvolume component tobe admixed therewith, thereby reducing the equipment cost whilenevertheless permitting precise metering of the quantities of the twocomponents and allowing a high mixing ratio.

The low-volume component may independently be maintained at any desiredtemperature and, of course, can be added to the high-volume componentwithout limitation on the ratio or the precision. This has been found tobe especially important for the rotational casting of caprolactamsystems. The terms rotation casting" is here used to refer to thecasting of a hardenable fluid mixture into a vessel constituting a flaskwhich is rotated about one or more axes so as to distribute the mixtureuniformly along the walls of the form. For the most part, rotationalcasting need not use centrifugal force for applying the mixture to theform wall, but rather may simply permit the distribution by adhesion ofa somewhat more viscous fluid.

The temperatures of the components and of the mixture and, therefore,the viscosity and the setting rate may be controlled within said rangesand the reaction time may be similarly altered, a factor which isimportant for obtaining products of the desired quality and uniformityof wall thickness. In practice, one may adjust both the temperature of acomponent or the mixture and the proportion of the activator during asingle rotational casting to obtain the uniformity.

According to features of the invention already discussed generallyabove, it is possible to provide volume ratios of caprolactam toactivator of 100 parts to 0.5 part or of caprolactam to catalyst of 100parts to 0.5 part (200:1 and more) by mixing the low-volume componentstogether (as an alternative to mixing one of these low-volume componentswith the high-volume components). In this case, the catalyst andactivator may be mixed together and circulated by a pump against theback pressure of an adjustable throttle downstream of the pump and of abypass into the mixing chamber. The throttle is adjusted to maintain theback pressure at atm. (approximately) below the injection-mixingpressure. This system guarantees synchronization of the mixing ofcatalyst and activator with the caprolactam. Both of the low-volumecomponents are then fed uniformly (with respect to one another) into themixing chamber uniformly over the mixing period.

The injection pressure which is established in the mixing head and whichserves to synchronously deliver the high-volume component and thelow-volume component to the mixing head may be provided by a cut-offvalve downstream of the bypass which, upon closing, causes the dynamicfluid column to be diverted from the circulation path into the mixingchamber. When the cut-off valve is reopened, circulation is restoredand, under the pressure differential, the mixing nozzles mayautomatically close. Each of the mixing nozzles is, to this end,provided with a differential-pressure valve or pressure-relieve valvewhich remains closed as long as the dynamic pressure head is 10atmospheres or more below the injection pressure but opens as thepressure rises to the injection pressure. Advantageously, thecirculation path of the principal component is similarly provided with acut-off valve which is synchronously and briefly operated to open itsbypass valve at the injection mixing pressure when .the cut-off valve ofthe low-volume component is closed.

According to yet another feature of the invention, the mixing head is aportable hand-held unit connected by flexible ducts with therecirculation paths, the flexible ducts preferably extending both to thestorage vessel or reservoir or the pump of the particular path, and tothe cut-off valve. Since the mixing temperature of the individualcomponents, especially the low-volume components, is important as adeterminant of the reaction time, the ducts leading to the mixing headand to the storage vessels are preferably heated or provided withinsulating sheaths while the storage vessel has an insulating jacketwhich likewise may be heated.

DESCRIPTION OF THE DRAWING The above and other objects, features andadvan tages of the present invention will be more readily apparent fromthe following description, reference being made to the accompanyingdrawing in which:

FIG. 1 is a diagrammatic elevational view of an apparatus for the mixingof two or more components of a system to be rotationally cast; and

FIG. 2 is a perspective view showing the rotationalcasting apparatus.

SPECIFIC DESCRIPTION FIG. I discloses an apparatus for the mixing of twocomponents, which comprises a large storage vessel I containingcaprolactam 20 preferably mixed with a catalyst if the catalyst has notbeen previously mixed with the activator. A stirrer 2 extends into thecaprolactam to ensure uniformity of heating and mixing thereof and thewall of the vessel 1 is thermally conductive and surrounded by a heatingjacket 4a to which a heating fluid such as hot water is supplied at 22,the depleted heating fluid being recovered at 24. The vessel 1 is thusof the double-wall type. A pump 5 communicates with the vessel 1 at thebase thereof and has anoutlet fitting 26 removably receiving a flexiblehose or tube 13. The latter is provided at an intermediate locationalong its length with a pressure-threshold valve 7 having a valveaperture 28 against which the conical plug 30 is held by a spring 32,the force constant of which determines the pressure threshold. The valveis designed to open against the force of the spring when the pressureahead of the aperture 28 reaches the injection-mixing pressure.

Valve 7 is provided on the mixing head 9 which comprises a mixingchamber 34 communicating with the valve, a spout 36 for discharging themixture, a switch button 38 for energizing the cut-off valves, and ahandle 40 enabling the head to be positioned in the mouth of arotation-casting mold.

The flexible tube 13 returns through a valve 10 which iselectromagnetically operable in response to the switch 38 and isconnected by the rigid tube 42 to the receptacle 1 to complete thecirculation path. If a substantial back pressure is desired for theprincipal component, a throttle valve may be provided in this line.

The low-volume component 44 is received in a small double-wall vessel 3which is provided with a heating jacket 4b supplied with heating fluidat 46, the depleted fluid being recovered at 48. A level-controllingdevice represented diagrammatically at 50 may be used to maintain thelevel of the low-volume component within the vessel 3. A rigid tube 53connected to vessel 3 delivers the low-volume component to a pump 6whose outlet fitting 54 is connected to a flexible tube 14 provided, ata location intermediate its ends, with the pres sure-threshold valve 8.This valve has an aperture 56 which is normally blocked by a valve body58 under the control of a spring 60. The return path extends through anelectromagnetically operated cut-off valve 11, triggered by switch 38and a throttle valve 12 which is adjustable to set the back pressure atabout atmospheres below the injection-mixing pressure. The tube portion62 and tube portion 64 of the return path are jacketed and a heatingfluid is circulated therethrough. The temperature of the heating fluidmay be regulated as represented at 66 and 68 to control the temperatureof the two components.

In operation, the pumps 5 and 6 are driven to circulate the twocomponents at the desired temperature and back pressures, whereupon theelectromagnetic valves 10 and 11 are closed by switch 38. Since thepumps 5 and 6 continue to operate, the pressure rapidly builds up to theinjection-mixing pressure whereupon the valves 7 and 8 open until thepressure rises in the mixing chamber 34 by virtue of the mixing of thetwo fluids at the elevated pressures therein. The valves 10 and 11 arethen opened, whereupon the pressure ahead of the valves 7 and 8 drops toterminate the mixing process.

In FIG. 2, we show a turntable 70 carrying a rotational casting mold 72and also supporting the vessels 1 and 3 as well as the mixing head 9.

SPECIFIC EXAMPLE A rotation casting having a volume of up to 10,000liters in the form of a hollw vessel, is cast from a caprolactam mixtureat a temperature of 120C. The caprolactam admixed with (catalyst) in avolume ratio of 200:1 to 200:0.6, is circulated at a rate in excess of50 kg/min through the pipe 13 at a back pressure of about 10 atmospheresgauge. The caprolactam mixture is maintained at a temperature of 120C bythe heating jacket. The activator is circulated at a back pressure ofabout 10 to atmospheres gauge through tube 14 at a rate of 0.250 to0.150 liters/minute as adjusted by the throttle 12. The valves 10 and 11are then closed to allow the injection-mixing pressure to build up to100/80 atmospheres gauge, whereupon over a period of about 120 seconds,the mixture is delivered to the eating mold. The latter is rotated atmore than 6 rpm and, after cooling, yields a highly uniform hollow body.It should be noted that the pressures are measured at the nozzles or arethe equivalent for rigid piping. Where the flexible tubing may expand,the controllable small activator quantity of 150 to 250 g/min. maycirculate with a pressure of 70/20 atm below the opening pressure of thevalve. Where a 2,000 liter vessel is to be produced, a single charge ofabout 50 kg may be used and cured for the indicated period. Where a10,000 liter vessel is made, eight charges of 50 kg each followed by 3minutes of curing can be used. In general the vessel is rotated at rpmabout the main axis and at 8 rpm about a secondary axis.

We claim:

I. A method of forming a mixture in a mixing chamber, comprising thesteps ofdisplacing a first fluid component along a path at a dynamicsuperatmospheric pressure; temporarily blocking the flow of said firstcomponent along said path while continuing the displacement thereof tobuild up pressure along said path to an injection-mixing pressure; andinjecting said first component into said mixing chamber when saidpressure along said path reaches said injection-mixing pressure andsimultaneously injecting a second fluid component into said mixingchamber.

2. The method defined in claim 1, further comprising the step ofcirculating said first component along a closed path and throttling thecirculation of said first component to produce said superatmosphericdynamic pressure. therealong.

3. The method defined in claim 1 wherein said superatmospheric dynamicpressure is about 10 atmospheres below said injection-mixing pressureand said second component is mixed in said chamber with said firstcomponent in a volume ratio of at least 200: l.

4. The method defined in claim 3 wherein said second component is alactam and said first component is selected from the group whichconsists of activators for polymerizing said lactam, catalysts forlactam polymerization and mixtures thereof.

5. The method defined in claim 4, further comprising the step of heatingsaid first component over a portion of said path.

6. The method defined in claim 5, further comprising the step ofcirculating said second component along a respective closed path.

7. An apparatus for forming a mixture, comprising means forming a mixingchamber; means forming a first path for dynamic displacement of a firstcomponent therealong under a dynamic superatmospheric pressure; apressure-responsive valve connecting said path with said chamber;cut'off means along said path downstream of said valve for temporarilyblocking said path and enabling buildup of pressure therein to aninjection-building pressure sufficient to enable said first component totraverse said valve and enter said mixing chamber; and injection meansfor introducing a second .fluid component into said mixing chambersimultaneously with the passage of said first component into the latter.

8. The apparatus defined in claim 7 wherein said path is closed fordisplacement of said first component in said mixing chamber and includesa receptacle for said first component, a pump connected between saidreceptacle and said valve and a throttle connected between said cut-offmeans and said receptacle.

9. The apparatus defined in claim 8 wherein said injection meansincludes a second circulating path for said second component, saidsecond circulating means including a vessel for said second component, apump connected to said vessel for displacing said second component, apressure threshold valve connected between said pump and said chamberand duct means connected between said pressure-threshold valve and saidvessel for returning the second component to the latter, and a cut-offvalve along said duct means operable synchronously with said cut-offmeans.

10. The apparatus defined in claim 9 wherein each of said paths includesflexible tubes connected to said chamber, said means forming saidchamber constituting a portable mixing head.

11. The apparatus defined in claim 9 wherein at least said path forcirculating said first component includes a heated conduit traversed bythe respective component 12. The apparatus defined in claim 9, furthercomprising means for heating said receptacle.

13. The apparatus defined in claim 9, further comprising means forheating said vessel.

14. The apparatus defined in claim 9 for rotational casting of a hollowbody with the mixture formed in said chamber, further comprising aturntable carrying a rotational casting mold, at least part of said pathbeing carried on said turntable.

15. The apparatus defined in claim 7 wherein said injection meansincludes means forming a second path for the dynamic displacement ofsaid second component therealong, each of said paths including arespective pump, a respective receptacle connected to each pump forreceiving the respective component from and supplying it to the pump,and a respective throttle valve in one of said paths between one of saidpumps and the respective receptacle, said one of said paths beingconnected to said mixing chamber between the respective pump and saidthrottle valve.

2. The method defined in claim 1, further comprising the step ofcirculating said first component along a closed path and throttling thecirculation of said first component to produce said superatmosphericdynamic pressure therealong.
 3. The method defined in claim 1 whereinsaid superatmospheric dynamic pressure is about 10 atmospheres belowsaid injection-mixing pressure and said second component is mixed insaid chamber with said first component in a volume ratio of at least200:1.
 4. The method defined in claim 3 wherein said second component isa lactam and said first component is selected from the group whichconsists of activators for polymerizing said lactam, catalysts forlactam polymerization and mixtures thereof.
 5. The method defined inclaim 4, further comprising the step of heating said first componentover a portion of said path.
 6. The method defined in claim 5, furthercomprising the step of circulating said second component along arespective closed path.
 7. An apparatus for forming a mixture,comprising means forming a mixing chamber; means forming a first pathfor dynamic displacement of a first component therealong under a dynamicsuperatmospheric pressure; a pressure-responsive valve connecting saidpath with said chamber; cut-off means along said path downstream of saidvalve for temporarily blocking said Path and enabling buildup ofpressure therein to an injection-building pressure sufficient to enablesaid first component to traverse said valve and enter said mixingchamber; and injection means for introducing a second fluid componentinto said mixing chamber simultaneously with the passage of said firstcomponent into the latter.
 8. The apparatus defined in claim 7 whereinsaid path is closed for displacement of said first component in saidmixing chamber and includes a receptacle for said first component, apump connected between said receptacle and said valve and a throttleconnected between said cut-off means and said receptacle.
 9. Theapparatus defined in claim 8 wherein said injection means includes asecond circulating path for said second component, said secondcirculating means including a vessel for said second component, a pumpconnected to said vessel for displacing said second component, apressure threshold valve connected between said pump and said chamberand duct means connected between said pressure-threshold valve and saidvessel for returning the second component to the latter, and a cut-offvalve along said duct means operable synchronously with said cut-offmeans.
 10. The apparatus defined in claim 9 wherein each of said pathsincludes flexible tubes connected to said chamber, said means formingsaid chamber constituting a portable mixing head.
 11. The apparatusdefined in claim 9 wherein at least said path for circulating said firstcomponent includes a heated conduit traversed by the respectivecomponent.
 12. The apparatus defined in claim 9, further comprisingmeans for heating said receptacle.
 13. The apparatus defined in claim 9,further comprising means for heating said vessel.
 14. The apparatusdefined in claim 9 for rotational casting of a hollow body with themixture formed in said chamber, further comprising a turntable carryinga rotational casting mold, at least part of said path being carried onsaid turntable.
 15. The apparatus defined in claim 7 wherein saidinjection means includes means forming a second path for the dynamicdisplacement of said second component therealong, each of said pathsincluding a respective pump, a respective receptacle connected to eachpump for receiving the respective component from and supplying it to thepump, and a respective throttle valve in one of said paths between oneof said pumps and the respective receptacle, said one of said pathsbeing connected to said mixing chamber between the respective pump andsaid throttle valve.